Agriculture For Beginners

The Rotation Of Crops

Doubtless you know what is meant by rotation, for your teacher has
explained to you already how the earth rotates, or turns, on its axis
and revolves around the sun. When we speak of crop-rotation we mean not
only that the same crop should not be planted on the same land for two
successive years but that crops should follow one another in a regular
order.

Many farmers do not follow a system of farming that involves a change of
crops. In some parts of the country the same fields are planted to corn
or wheat or cotton year after year. This is not a good practice and
sooner or later will wear out the soil completely, because the
soil-elements that furnish the food of that constant crop are soon
exhausted and good crop-production is no longer possible.

Why is crop-rotation so necessary? There are different kinds of plant
food in the soil. If any one of these is used up, the soil of course
loses its power to feed plants properly. Now each crop uses more of some
of the different kinds of foods than others do, just as you like some
kinds of food better than others. But the crop cannot, as you can, learn
to use the kinds of food it does not like; it must use the kind that
nature fitted it to use. Not only do different crops feed upon different
soil foods, but they use different quantities of these foods.

Now if a farmer plant the same crop in the same field each year, that
crop soon uses up all of the available plant food that it likes. Hence
the soil can no longer properly nourish the crop that has been year by
year robbing it. If that crop is to be successfully grown again on the
land, the exhausted element must be restored.

This can be done in two ways: first, by finding out what element has
here been exhausted, and then restoring this element by means either of
commercial fertilizers or manure; second, by planting on the land crops
that feed on different food and that will allow or assist kind Mother
Nature "to repair her waste places." An illustration may help you to
remember this fact. Nitrogen is, as already explained, one of the
commonest plant foods. It may almost be called plant bread. The wheat
crop uses up a good deal of nitrogen. Suppose a field were planted in
wheat year after year. Most of the available nitrogen would be taken out
of the soil after a while, and a new wheat crop, if planted on the
field, would not get enough of its proper food to yield a paying
harvest. This same land, however, that could not grow wheat could
produce other crops that do not require so much nitrogen. For example,
it could grow cowpeas. Cowpeas, aided by their root-tubercles, are able
to gather from the air a great part of the nitrogen needed for their
growth. Thus a good crop of peas can be obtained even if there is little
available nitrogen in the soil. On the other hand wheat and corn and
cotton cannot use the free nitrogen of the air, and they suffer if there
is an insufficient quantity present in the soil; hence the necessity of
growing legumes to supply what is lacking.

Let us now see how easily plant food may be saved by the rotation of
crops.

If you sow wheat in the autumn it is ready to be harvested in time for
planting cowpeas. Plow or disk the wheat stubble, and sow the same field
to cowpeas. If the wheat crop has exhausted the greater part of the
nitrogen of the soil, it makes no difference to the cowpea; for the
cowpea will get its nitrogen from the air and not only provide for its
own growth but will leave quantities of nitrogen in the queer nodules of
its roots for the crops coming after it in the rotation.

If corn be planted, there should be a rotation in just the same way. The
corn plant, a summer grower, of course uses a certain portion of the
plant food stored in the soil. In order that the crop following the corn
may feed on what the corn did not use, this crop should be one that
requires a somewhat different food. Moreover, it should be one that fits
in well with corn so as to make a winter crop. We find just such a
plant in clover or wheat. Like the cowpea, all the varieties of clover
have on their roots tubercles that add the important element, nitrogen,
to the soil.

From these facts is it not clear that if you wish to improve your land
quickly and keep it always fruitful you must practice crop-rotation?

AN ILLUSTRATION OF CROP-ROTATION

Here are two systems of crop-rotation as practiced at one or more
agricultural experiment stations. Each furnishes an ideal plan for
keeping up land.

In these rotations the cowpeas and clovers are nitrogen-gathering crops.
They not only furnish hay but they enrich the soil. The wheat, corn, and
cotton are money crops, but in addition they are cultivated crops; hence
they improve the physical condition of the soil and give opportunity to
kill weeds. The grasses and clovers are of course used for pasturage and
hay. This is only a suggested rotation. Work out one that will meet your
home need.

=EXERCISE=

Let the pupils each present a system of rotation that includes the
crops raised at home. The system presented should as nearly as
possible meet the following requirements: